Compositions and methods for curing concrete

ABSTRACT

A composition that may be used to retain moisture within fresh concrete as it cures to optimize the curing of the concrete may include one or more hardening and densifying agents and one or more temporary moisture sealing agents. Additionally such a composition may include a siliconate. The hardening and densifying agent of such a composition may penetrate the surface of fresh concrete to react with free lime, providing the fresh concrete with a strong surface. The temporary moisture sealing agent may form a moisture barrier on the surface of the fresh concrete to prevent moisture from escaping from the fresh concrete before the fresh concrete has sufficiently cured. The temporary moisture sealing agent may degrade within a matter of days, facilitating its removal from the surface of the concrete once the concrete has cured and enabling further treatment of the surface without undue delay.

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/299,880, filed on Jan. 29, 2010, titled COMPOSITIONS AND METHODSFOR CURING CONCRETE, the entire disclosure of which is, by thisreference, hereby incorporated herein.

TECHNICAL FIELD

The present invention relates generally to compositions and methods forcuring concrete and, more specifically, to compositions that holdmoisture within concrete as the concrete cures, as well as to methodsfor retaining moisture within concrete as it cures. Specifically, thepresent invention includes compositions and methods in which a hardeningand densifying agent is used in curing concrete, including, withoutlimitation, concrete structures, such as slabs, pavement, runways anddecks (e.g., bridges, parking structures, etc.).

BACKGROUND OF RELATED ART

Concrete typically includes cement, fly ash, and an aggregate (e.g.,sand, limestone, gravel, etc.), among other possible components (e.g.,chemical admixtures, etc.). When water is added to the cement, achemical reaction known as “hydration” occurs between the cement and thewater. The resulting cement gel or paste cures, or sets, to bind theother components of the concrete together. The longer the cement isexposed to water, the more complete and consistent (e.g., even) thehydration reaction throughout the concrete. Initially, the cement gel orpaste is rigid, but not very strong. If water is removed from the cementgel or paste (e.g., by evaporation, etc.) before the cement gel or pastegains sufficient strength, the resulting structural changes to theconcrete (e.g., shrinkage, etc.) may cause the cement and, thus, theconcrete, to be undesirably porous, to crack, or to otherwise weaken.Accordingly, it is often desirable to maintain a suitable water, ormoisture, content within fresh concrete until the cement gel or pastehas had sufficient time to gain strength.

A number of techniques have been developed to maintain the moisturecontent of fresh concrete as the cement within the fresh concrete cures,or strengthens. One common technique involves trapping water within thefresh concrete by providing a moisture barrier on the exposed surfacesof the fresh concrete. Common moisture barriers include resinous (e.g.,acrylic, etc.) concrete curing compositions. Unfortunately, manyconventional resinous concrete curing compositions do not provide anaesthetically pleasing finished surface, and they are difficult toremove. Even so-called “self-dissipating” compositions, which typicallydegrade when exposed to ultraviolet (UV) radiation over long periods oftime (e.g., 40 to 60 days or longer), leave finished concrete surfaceswith aesthetically undesirable appearances and are difficult to removewhen further surface treatment (e.g., hardening and densifying,polishing, application of sealers, etc.) is desired.

SUMMARY

The present invention includes compositions that may be used to retainmoisture within fresh concrete as it cures to optimize curing of theconcrete. For the sake of simplicity, the compositions of the presentinvention are referred to herein as being useful for curing concrete.

A composition suitable for curing concrete may include a hardening anddensifying agent. Examples of such an agent include, but are not limitedto, silicates. As used herein, silicates include polysilicates (e.g.,alkali metal polysilicates, such as lithium polysilicate, sodiumsilicate, potassium silicate, etc.) and colloidal silicas. The abilityof the hardening and densifying agent to reduce porosity in exposedsurfaces of fresh concrete may, in effect, cause the fresh concrete toretain moisture for prolonged periods of time, which may enhance or evenoptimize curing of the fresh concrete.

In some embodiments, a composition of the present invention may consistof the hardening and densifying agent. In other embodiments, acomposition may consist essentially of the hardening and densifyingagent.

Other embodiments of compositions that are suitable for curing concretein accordance with teachings of the present invention may include, oreven consist essentially of, a hardening and densifying agent and asiliconate (e.g., a metal siliconate; an alkali metal siliconate, suchas potassium methyl siliconate; etc.). In addition to hardening anddensifying concrete, some siliconates are known to form polymeric filmson surfaces to which they are applied. Such a polymeric film may enhancethe ability of the hardening and densifying agent to trap moisturewithin fresh concrete.

Another embodiment of a composition of the present invention includes atemporary moisture sealing agent in addition to a hardening anddensifying agent and, optionally, a siliconate. When such an embodimentof composition is applied to a surface of fresh concrete, the temporarymoisture sealing agent forms a substantially confluent (i.e.,substantially non-porous) film over the surface. A film formed by thetemporary moisture sealing agent acts as a moisture barrier, preventingwater from escaping the temporarily sealed surface on which the film hasbeen formed. In some embodiments, a temporary moisture sealing agent maydegrade within days (e.g., three days, seven days, 14 days, less than amonth, etc.) of its application to a concrete surface, enablingself-dissipation or simplifying its removal from the surface, andenabling further treatment of the surface without any significant timedelay after the concrete has sufficiently cured.

A composition that includes or consists essentially of any of theforegoing may also include one or more non-essential components. Withoutlimiting the scope of the present invention, non-essential componentsmay include pigments, surfactants and leveling agents.

Concrete curing systems that include separate components are also withinthe scope of the present invention. In some embodiments, such a concretecuring system may include one component that includes hardening anddensifying agent and, optionally, a siliconate, while a separatecomponent includes a temporary moisture sealing agent.

The present invention also includes various embodiments of methods forformulating and manufacturing compositions that may be used to cureconcrete. In a manufacturing method, a hardening and densifying agentmay be blended with one or more substances, such as a siliconate or atemporary moisture sealing agent, that will retain moisture within freshconcrete as the fresh concrete cures.

In addition, the present invention includes methods for curing concrete.Such a method includes applying a composition that includes a hardeningand densifying agent to an exposed surface of the concrete. Thehardening and densifying agent may be applied alone, or with one or moreother substances that will retain moisture within the fresh concrete. Asa non-limiting example, the hardening and densifying agent may beapplied with a siliconate. As another example, the hardening anddensifying agent may be applied with a temporary moisture sealing agent.In embodiments where the hardening and densifying agent is applied to asurface of fresh concrete along with another substance that retainsmaterial within the fresh concrete, application of the hardening anddensifying agent may be effected before the other substance forms a filmor barrier on the surface. In some embodiments, the hardening anddensifying agent may be applied before the other substance,substantially concurrently with the other substance, or as part of thesame composition as the other substance. In other embodiments, thehardening and densifying agent may be applied to the surface after theother substance, but before the other substance forms a barrier on thesurface (e.g., polymerizes, agglomerates, etc.).

Other aspects, as well various other features and advantages ofdifferent aspects, of the present invention will become apparent tothose of skill in the art through consideration of the ensuingdescription and the appended claims.

DETAILED DESCRIPTION

A composition that is suitable for preventing moisture from escapingfresh, curing concrete (i.e., for use in curing concrete) in accordancewith teachings of the present invention, in various embodiments,includes a hardening and densifying agent. Some embodiments of such acomposition further include a siliconate. In other embodiments, acomposition of the present invention may additionally include atemporary moisture sealing agent.

The hardening and densifying agent of a composition of the presentinvention may comprise, consist essentially of or consist of apolysilicate. More specifically, the polysilicate may include a metalpolysilicate. In even more specific embodiments, the metal polysilicatemay comprise one or more alkali metal polysilicates, such as lithiumpolysilicate. The polysilicate may make up about 10% to about 20% of thetotal weight (i.e., w/w) of a composition of the present invention.These percentages are based upon the polysilicate-containing productused in the composition. As polysilicates are typically provided inliquid form, the percentages represent the amount of liquid, regardlessof the solids content of that liquid, used in a composition of thepresent invention. In embodiments where LUDOX® lithium polysilicate isobtained from Grace Davison of Columbia, Md., the actual solids (i.e.,lithium polysilicate) content of that product is about 20% solids, byweight (w/w), meaning that the actual lithium polysilicate content of acomposition of the present invention is about 2% to about 4% of thetotal weight of the composition (i.e., about 10%×20% to about 20%×20%).

As an alternative to a polysilicate or mixture of polysilicates, thehardening and densifying agent of a composition that incorporatesteachings of the present invention may include, consist essentially ofor consist of a colloidal silica, such as a cationic amorphous silica.Like polysilicates, colloidal silicas are often obtained in liquid form.For example, the colloidal silica suspension available from GraceDavison as LUDOX® HSA has a silica content of 29.0% to 31.0%, by weightof the solution. Thus, a composition that includes that type ofcolloidal silica may have an actual colloidal silica content of about2.9% w/w (i.e., about 10%×29.0%) to about 6.2% w/w (i.e., about20%×31.0%).

Of course, compositions that include mixtures of different types ofhardening and densifying agents, including different silicates, are alsowithin the scope of the present invention.

In embodiments where a composition of the present invention includes asiliconate, the siliconate may comprise about 3% to about 6% of theweight of the composition. In some embodiments, the siliconate maycomprise a metal siliconate. In more specific embodiments, thesiliconate may comprise an alkali metal siliconate, such as potassiummethyl siliconate. As an example, the potassium methyl siliconate of acomposition of the present invention may comprise the “silane resinsolution” available from Dow Corning Corporation of Midland, Mich., asXIAMETER® OFS 0777 SILICONATE. That solution has a solids content of 40%to 70% w/w. Thus, the actual potassium methyl siliconate solids may makeup about 1.2% (i.e., about 3%×40%) to about 4.2% (i.e., about 6%×70%) ofthe weight of the composition.

Silicates and other hardening and densifying agents may facilitatecuring of concrete without the need for subsequent removal, or requiringonly a minimal removal effort (e.g., spraying with water, lightbrushing, etc.).

The temporary moisture sealing agent of the curing compound may beselected and/or configured to remain in place for a few days, and thenbe removed with little or no additional effort. It may eventually breakdown and dissipate once the fresh concrete has sufficiently cured.Examples of a temporary moisture sealing agent that may be used invarious embodiments of compositions and methods that incorporateteachings of the present invention include, without limitation,materials that will degrade in a matter of days (e.g., three days, sevendays, fourteen days, etc.). In some embodiments, such a material mayinclude a wax, such as a paraffin wax, a polyethylene wax, a scale waxor the like.

The temporary moisture sealing agent may be included in a composition inan amount that will enable it to form a substantially confluent filmover a surface to which the composition is applied. In some embodiments,about 30% to about 60% of the weight of a composition may comprise atemporary moisture sealing agent. A specific, but non-limiting, exampleof a wax that may be used in a composition of the present invention isthe paraffin wax available from Michelman, Inc., of Cincinnati, Ohio, asMICHEM® LUBE 743. That material has a solids content of 35% to 50%,which would equate to about 10.5% (i.e., about 30%×35%) to about 30%(i.e., about 60%×50%) of a composition of the present invention. Inother embodiments, the temporary moisture sealing agent may comprise ascale wax, such as MICHEM® EMULSION 70750 or MICHEM® EMULSION 39235,both of which are available from Michelman, Inc.

A specific embodiment of a composition of the present invention includes(or may consist of) about 10% to about 20%, by weight, lithiumpolysilicate or colloidal silica; about 3% to about 6%, by weight,potassium methyl siliconate; and about 30% to about 60%, by weight, wax,with the balance (e.g., about 14% to about 69%, by weight) of thecomposition comprising water.

In other embodiments, a composition of the present invention may consistof a temporary moisture sealing agent, a hardening and densifying agent(e.g., a silicate and/or colloidal silica), and, optionally, water.

As an alternative to a wax, a variety of other membrane or film formingtemporary moisture sealing agents may be used in a composition thatincorporates teachings of the present invention. Non-limiting examplesof other temporary moisture sealing agents include oils and oil basedcuring compounds, polyvinyl alcohol (PVA) based curing compounds,chlorinated rubber curing compounds, resin based curing compounds, andother materials and compounds that will form a temporary membrane orfilm over a surface of fresh concrete to seal moisture within the freshconcrete as it cures. Another embodiment of temporary moisture sealingagent includes water-soluble film-forming polymers, such as thosedescribed by U.S. Patent Application Publication 2009/0162540 ofGolovkova, et al., the entire disclosure of which is, by this reference,hereby incorporated herein. Other materials, such as chloroparaffins,fatty acid triglycerides, alkyl sulfonic esters (e.g., phenols,cresoles, fatty acid esters, etc.), phthalates (e.g., dioctyl phthalate,dibutyl phthalate, benzyl butyl phthalate, etc.), polymers derived fromglycerol, polymers derived from iso-cyanates or thio-cyanates (e.g.,polyurethane, vegetable oil-extended polyurethane systems,moisture-curable polyurethane polymers, etc.). polymers derived fromsulfur-containing reactants and polymers derived from silicon-containingreactants may be used as temporary moisture sealing agents.

In addition to the foregoing components, as well as various combinationsthereof, one or more other components may also be included in acomposition according to the present invention. Non-limiting examples ofsuch components include surfactants. leveling agents and pigments. Inembodiments where a hardening and densifying agent is mixed with atemporary moisture sealing agent, a surfactant may enable these twocomponents to homogeneously or substantially homogeneously blend withone another. A leveling agent may facilitate spreading of a compositionof the present invention over a surface of a substrate to be cured. Apigment may serve a variety of functions, including, without limitation,providing an identifier of the state of a substrate (e.g., an indicatorthat the substrate has not cured, etc.), light reflectance (e.g., when awhite or other light colored pigment is used) and the like.

The present invention also includes methods for compounding acomposition for use in curing concrete. In various embodiments, such amethod includes providing a volume of water, blending at least onehardening and densifying agent into the volume of water, then blendingat least one temporary moisture sealing agent into the volume of water.Blending may be effected using substances (e.g., the hardening anddensifying agent and the temporary moisture sealing agent, etc.) thatare already in solution (e.g., aqueous based substances, etc.).

In some embodiments, a siliconate or mixture of siliconates may beblended into the composition. The siliconate or siliconates may be addedafter the hardening and densifying agent has been mixed with the waterand/or before the temporary moisture sealing agent is blended with thewater and the hardening and densifying agent.

In a specific embodiment, a volume of water is provided that correspondsto about 14 percent to about 69 percent of a total weight of the desiredfinished composition. At least one hardening and densifying agent isthen mixed into the volume of water, with the amount of the hardeningand densifying agent being sufficient to comprise about 10 percent toabout 20 percent of the total weight of finished composition.Thereafter, a sufficient amount of at least one siliconate may beblended into the mixture such that about three percent to about sixpercent of the total weight of the finished composition will comprisethe at least one siliconate. Finally, at least one temporary moisturesealing agent is blended into the mixture. The amount of the temporarymoisture sealing agent may be sufficient to comprise about 30 percent toabout 60 percent of the total weight of the finished composition. Theresulting composition may then be packaged, stored, and transported inany suitable manner known in the art.

In addition, the present invention includes methods for curing concrete.Such a method includes applying a composition that includes a hardeningand densifying agent to an exposed surface of the concrete. Thehardening and densifying agent may be applied alone, or with one or moreother substances that will retain moisture within the fresh concrete. Asa non-limiting example, the hardening and densifying agent may beapplied with a siliconate. As another example, the hardening anddensifying agent may be applied with a temporary moisture sealing agent.In embodiments where the hardening and densifying agent is applied to asurface of fresh concrete along with another substance that retainsmaterial within the fresh concrete, application of the hardening anddensifying agent may be effected before the other substance forms a filmor barrier on the surface. In some embodiments, the hardening anddensifying agent may be applied before the other substance,substantially concurrently with the other substance, or as part of thesame composition as the other substance. In other embodiments, thehardening and densifying agent may be applied to the surface after theother substance, but before the other substance forms a barrier on thesurface (e.g., polymerizes, agglomerates, etc.).

As the hardening and densifying agent and the temporary moisture sealingagent may be applied separate, the present invention also includesconcrete curing systems in which these components are separate from oneanother.

The ability of a composition or system of the present invention toretain moisture within fresh concrete were evaluated by a knowntechnique—the ASTM C 156 (2005) test protocol from ASTM International.The ASTM C 156 (2005) is a test protocol titled “Water Retention byLiquid Membrane-Forming Curing Compounds for Concrete” that determinesthe ability of various compounds to prevent moisture from escaping freshconcrete. Generally, the tested composition was applied to finishedsurfaces of fresh concrete slabs and the weight loss of each sample wasmeasured after a predetermined duration of time.

More specifically, “standard” mortar was mixed. “Standard” mortarincludes ASTM C 150 Type I/II Portland cement, ASTM C 778 standardgraded sand, and water. The water-to-cement ratio of the mixture was 0.4and the sand-to-cement ratio of the mixture was 2.19. The average flowof the mixture, which was measured in accordance with the protocol setforth by ASTM C 87, was 40.

The mortar mixture was used to prepare three two inch thick squaremortar specimens with 39.1 sq. in. top surfaces for the testedcomposition, and three more mortar specimens to serve as a control. Thesurface of each mortar specimen was steel troweled. The edges of eachspecimen were sealed with paraffin wax, providing a test surface with anarea of about 36 sq. in.

Shortly after the edges were sealed, the test composition was applied,by brush, to the surfaces of three corresponding mortar specimens. Thetested composition was applied to the surface of each of the threemortar specimens in an amount equivalent to one gallon per 400 sq. ft.Nothing was applied to the surfaces of the three mortar specimens thatserved as controls during the test. At this point, each mortar specimenwas placed in a special controlled humidity chamber (with a temperatureof 100°±2° F., a relative humidity of 32% ±2%, and a water evaporationrate of 2 gal./hour) and weighed. The mortar specimens were thenpermitted to cure in the chamber for another 72 hours, at which pointthe weight of each mortar specimen was again determined. The finalweighing indicated the weight loss, due to water evaporation, of eachmortar specimen. The three weight loss numbers corresponding to eachcontrol and the three weight loss numbers corresponding to each testedcomposition were averaged, and the data that corresponded to the testedcomposition was compared to the data that corresponded to the control.The tested composition performed well within the parameters set by thetest. Specifically, the tested composition exhibited an average massloss of 0.45 kg/m² (0.092 lb/ft²), which is well within the 0.55 kg/m²(0.113 lb/ft²) mass loss limit set by ASTM C 156 (2005), indicating thata composition that incorporates teachings of the present invention issuitable for use in curing concrete.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some embodiments. Similarly, otherembodiments of the invention may be devised which do not exceed thescope of the present invention. Features from different embodiments maybe employed in combination. The scope of the invention is, therefore,indicated and limited only by the appended claims and their legalequivalents, rather than by the foregoing description. All additions,deletions and modifications to the invention as disclosed herein whichfall within the meaning and scope of the claims are to be embracedthereby.

What is claimed:
 1. A composition useful for curing concrete,comprising: a hardening and densifying agent; and a temporary moisturesealing agent comprising a material that forms a film on a surface ofthe concrete without substantially entering into pores in the surface ofthe concrete and that will break down and self-dissipate to facilitateits complete removal from the surface of the concrete less than a monthafter its application as a film to the surface of the concrete.
 2. Thecomposition of claim 1, wherein the hardening and densifying agentcomprises at least one silicate.
 3. The composition of claim 2, whereinthe at least one silicate comprises at least one of lithiumpolysilicate, sodium silicate and potassium silicate.
 4. The compositionof claim 2, further comprising at least one siliconate.
 5. Thecomposition of claim 4, wherein the at least one siliconate comprisespotassium methyl siliconate.
 6. The composition of claim 4, wherein: thehardening and densifying agent includes: the at least one silicatecomprising about 10 percent to about 20 percent of a total weight of thecomposition; and the at least one siliconate comprising about threepercent to about six percent of the total weight of the composition; thetemporary moisture sealing agent comprises about 30 percent to about 60percent of the total weight of the composition; and further comprisingwater.
 7. The composition of claim 6, wherein the water comprises abalance of the total weight of the composition.
 8. The composition ofclaim 1, wherein the hardening and densifying agent comprises colloidalsilica.
 9. The composition of claim 8, wherein the hardening anddensifying agent further comprises at least one siliconate.
 10. Thecomposition of claim 8, wherein: the hardening and densifying agentincludes: the colloidal silica comprising about 10 percent to about 20percent of a total weight of the composition; and the at least onesiliconate comprising about three percent to about six percent of thetotal weight of the composition; the temporary moisture sealing agentcomprises about 30 percent to about 60 percent of the total weight ofthe composition; and further comprising water.
 11. The composition ofclaim 1, wherein the temporary moisture sealing agent comprises wax. 12.The composition of claim 11, wherein the wax comprises at least one of aparaffin wax, a polyethylene wax, and a scale wax.
 13. The compositionof claim 1, wherein the temporary moisture sealing agent comprises atleast one of an oil or oil based curing compound, a polyvinyl alcohol(PVA) based curing compound, a chlorinated rubber curing compound, and aresin based curing compound.
 14. The composition of claim 1, wherein thetemporary moisture sealing agent comprises a water-soluble film-formingpolymer.
 15. The composition of claim 1, wherein the temporary moisturesealing agent comprises at least one of a chloroparaffin, a fatty acidtriglyceride, an alkyl sulfonic ester, a phthalates, a polymer derivedfrom glycerol, a polymer derived from an iso-cyanate or a thio-cyanates,a polymer derived from a sulfur-containing reactant and a polymerderived from a silicon-containing reactant.
 16. The compound of claim 1,wherein the temporary moisture sealing agent is blended with thehardening and densifying agent.